[bdp24]

I haven't seen this topic addressed, so let me ask.....is it a good idea to glue two 3/4" MDF panels together (for a double-thick baffle) with Green Glue instead of regular white or yellow glue?

[Skiman]

Green glue is marketed as a sound deadener, i.e. it will absorb the vibrations that sound creates when it impacts a hard surface. My home theater was designed by Rives audio, and green glue was specified and used between double drywall. In addition to reducing the sound transmitted through the walls, it acts to reduce the reflected sound inside the room. Is this ability what you want in your application?

http://www.greengluecompany.com/benefit/how-green-glue-works

[Early B.]

Aw, geez. Wait for it .... some geeky forum member is gonna request an A/B test of the sonic differences between various glues.

[Peter J]

I haven't seen this topic addressed, so let me ask.....is it a good idea to glue two 3/4" MDF panels together (for a double-thick baffle) with Green Glue instead of regular white or yellow glue?

Despite the name, Green Glue is not glue in the sense that you could stick things together with it.  It's intended to damp vibrational energy between 2 layers of...well, material...primarily drywall. It would be better described as green goo, 'cuz that's how it will remain, gooey!

 It has no structural fastening capability so mechanical fastening is nesessary between outer layers of a constrained layer assembly.

 To answer your question,  there would be better ways to accomplish panel damping on a speaker cabinet. That's what the non-foam layer of NoRez does, plus there are many others. Google panel damping  or constrained layer for more info than you probably want!

[alch3my]

Green Glue does not bond 2 panels together rigidly. I have done some experiments of my own to see how effective it dampens vibrations and it is AMAZING.

This is the video from the manufacturer:
http://www.youtube.com/watch?v=LiUBxjFG53o

My video:
http://www.youtube.com/watch?v=t157574I7gE
In real life, the difference is more startling. For my test panels, the 2 mdf pieces are held together only by the green glue and nothing else. When I'm about to start my speaker project, i'll bond the two pieces together using GG, and glue the pieces together near the edges

[Peter J]

When I'm about to start my speaker project, i'll bond the two pieces together using GG, and glue the pieces together near the edges

That's an interesting idea. So perimeter will be conventional glue, center of panel Green Glue? I'm wondering if there's a point where the Green glue film thickness compromises its effectiveness. It'd get pretty skinny in a clamped assembly.  Have you experimented with such an assembly?

[goskers]

I would not recommend gluing the outer portion as you will greatly reduce the shearing of the panels.  There are some general construction glues which stay pliable in their set state.  These might be viable alternatives to the more expensive green glue.

[bdp24]

Thanks Peter, that's exactly what I wanted to find out. I'm having two sub cabinets made, and I was wondering if Green Glue could be used in the construction of them, to glue panels together. And the answer is.....no!

[glynnw]

Please don't make the same mistake I did - I used a house brand imitation green glue from an online acoustic supplier to glue two 3/4" plywood together for an open baffle.  The stuff never dried - the two pieces slid apart after sitting for 48 hours.  I secured them to each other with screws and for the next several months the stuff continued to seep out even as I used them for speaker baffles, despite many attempts to seal it in.  Finally I replaced the baffles - they are currently sitting in a field in north Louisiana to see if a summer outside here will harden the glue.

[bdp24]

Thanks for the warning. I'm sticking to regular ol' carpenter's glue, and will do panel damping another way.

[Peter J]

I would not recommend gluing the outer portion as you will greatly reduce the shearing of the panels.  There are some general construction glues which stay pliable in their set state.  These might be viable alternatives to the more expensive green glue.

I think you mean shear strength, correct? Seems to me there would be so little shear force in a speaker box that it would be a non-factor. Even so, I'd agree with you on looking at other methods for panel damping...why reinvent the well researched wheel?

 I have used polyurethane constuction adhesive in speaker cabinets, and it will have a thicker glue line than wood glue but it won't acheive the same level of panel damping as Green Glue. It also needs to be constrained until it sets because of expansive properties, ask me how I know

It is an interesting idea, but my gut tells me that the damping properties of Green Glue would be largely mitigated if glue line were the same thickness as wood glue.

[Funnehaha]

Anybody want to know what this "Green Glue" stuff is? If so, maybe I can help.

What does it say are its ingredients on the label? Is it water-based or solvent-based? Any odor?

Let me know...

[Peter J]

Anybody want to know what this "Green Glue" stuff is? If so, maybe I can help.

What does it say are its ingredients on the label? Is it water-based or solvent-based? Any odor?

Let me know...

It's magic fairy goo!

 There's no ingredients on the tube because it's not food and I'm sure they want to protect their market.  Mild warnings for skin contact, water based, low odor. Seems very benign. Oh, and it's green! Actually kind of a mint green...

[rajacat]

This marine adhesive stays flexible after curing and no fasteners needed. This stuff is tenacious and ultra strong.... definitely overkill in the strength dept. Available in a selection of colors; fast or slow cure.

http://www.westmarine.com/webapp/wcs/stores/servlet/Product2_11151_10001_21280_-1____ProductDisplayErrorView#.UBk6x2G0zr4

[richidoo]

I built horn speakers with MDF and titebond 1 then clad another layer on the 1'x4' sidewalls with green glue. I troweled on a layer to each mating surface, pressed them firmly, and shot a few staples in the center and each corner.  I masked off a 1 inch border on the edge of the mating surfaces with blue tape, trowelled on the green glue, then removed the mask.

The ringing of the MDF was very strongly damped.   Maybe it would have been just as damped with gluing them together with epoxy? Who knows.

The speakers were used inside on the carpet for a year and no green glue ever crept to the edges. The edges were not sealed or glued with other glue. Green glue soaks liquid into the substrate then it gets very viscous. Adhesion holds it in the thin layer without creeping. The holding strength in an application like this is very strong, but it is not structural.

[rajacat]

OTOH maybe you don't want a strong adhesive for a "constrained" layer even if it maintains its flexibility. Perhaps if the layer is too strongly attached on either side it loses some of its sound deadening qualities and become just another layer and not performing the constraining function.

[Hank]

Everybody:  use the 3M adhesive and 3M blue painters tape and make me happy